Such a pipe is intended to convey a cryogenic fluid for example coming from a gas liquefaction method. The conveyed fluid is for example liquefied natural gas having a boiling temperature below 163° C.
More generally, a cryogenic fluid conveyed by the pipe has a boiling temperature below 0° C.
Natural gas extracted from the ground is a significant source of fuel that can be exploited.
It is known to use pipelines to convey natural gas in gaseous form from its production site to its exploitation site. However, in many cases, in particular when the production site is located in an expanse of water, it is simpler and more cost-effective to convey the natural gas in liquid form, so as to decrease its volume during transport and facilitate its storage and handling.
However, the handling of cryogenic fluids, and in particular the unloading of a cryogenic fluid from a liquefaction plant toward a carrier ship, or from a carrier ship toward a land-based storage facility, must be done near the coast, often using articulated connecting arms connecting the ship to the plant or the storage facility.
Such articulated arms are not suited to cases where the loading or unloading operations are done far from the coast, in relatively unprotected areas, in particular when the liquefaction units are located on floating facilities of the FLNG type.
In that case, the liquefied natural gas can only be unloaded when the weather conditions are calm, which makes the exploitation difficult.
Furthermore, the flexible pipes of the connected or not connected type known for unloading hydrocarbonaceous fluids at ambient temperature are not able to convey cryogenic fluids at temperatures below −40° C./−50° C., given the very low temperatures of the cryogenic fluids and their particular properties.
To offset this problem, EP 1 945 983 describes a flexible pipe provided to convey cryogenic fluid.
Such a pipe comprises a non-sealed stapled inner tube offering resistance to the outside pressure. This pipe comprises, from the inside toward the outside, an inner shell designed to withstand the outside pressure, an impermeable layer made up of a fine polymer film in direct contact with the shell, a layer of insulation, and a plastic sheath withstanding low temperatures. The insulation layer makes it possible to create a sufficient heat gradient to be covered by the plastic sheath. The stapled inner tube is covered with insulation and outwardly reinforced by a pressure arch and tensile armor layers.
To ensure proper thermal insulation and prevent the cryogenic fluid from heating or ice from forming on the outside of the flexible pipe, thermal insulation layers are provided around the tensile armor layers to keep the contact surface of the flexible pipe with the water at a high enough temperature to avoid the formation of ice.
However, such a structure is not fully satisfactory due to the complexity of its inner structure.
A flexible pipe by the Applicant for conveying cryogenic fluid is described in “LNG Transfer—Cryogenic flexible pipe for transfer—May-June 2000.” This flexible pipe comprises, from the inside toward the outside, a corrugated tube that can seal against the cryogenic fluid and ensure resistance to the internal pressure, tensile armor layers able to bear the axial loads applied on the pipe, and a set of thermal insulation layers.
However, such flexible pipes are not fully satisfactory with regard to the pressure loss of the fluid circulating in the pipe. These pipes are therefore only usable in practice over a relatively small length, which can make its industrial use difficult.